Digester



M y 5, 1931. P. G. VON HILDEBRANDT 1,803,444

DIGESTBR Filed Nov. 20, 1928 INVENTOR WITNESSES lulose fibers.

Patented May 5, 1931 unrraa s'raras PATENT OFFICE PAUL G. VON HILDEBRANDT, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO HOWARD B. SALKELD, OF PITTSBURGH, PENNSYLVANIA.

mem'mn Application filed November 20, 1928. Serial No. 320,602.

The invention relates to digesters for use in making pulp from ligno-cellulose mate- 19 applicable to any kind of wood and wood waste, which reduces digestion time and increases pulpyields, and which is of simple, sturdy construction and easy to operate.

A special object of the invention is to provide a di estion a aratus for use in a wood fibrat-ion process disclosed and claimed in a copending application, Serial No. 320,601, filed by me November 20, 1928.

The invention may be described in connec- 553 tion with the accompanying drawings, in

which Fig. 1 is a vertical elevation, partly in section, showing the preferred embodiment,

and Figs. 2 and dare horizontal sections taken respectively on lines IIIl[ and ly charged in a digester', with a reagent for dissolving the incrustants which bind the cel- The material was thus free to expand and to be agitated by the steam or other fluid formed in digestion. The yields are low, the digestions are relatively long, and the fibers suffer from certain disadvantages.

For example, soda fibers are too short for many purposes; While sulfite fiber is long, but harsh;

In a copending application I have disclosed and claimed a process of making pulp from wood which produces long soft fiber, reduces digestion time, and by which the yields of pulp are materially increased. That invention is predicated upon my discovery that the disadvantages of prior processes, and especially the soda process, are due in part to slow penetration of the vigorous solvent used, and in part to agitation of the mass during digestion. lhose disadvantages are, in accordance with the invention referred to, substantially overcome by first opening the grain of the wood without removing any substantial amount of incrustants, and subsequently digestin g the softened material with a vigorous incrustant solvent, such as soda, while mechanically compressing the mass, whereby the chemically disruptive action of the reagent and the comminuting action of agitation upon the fibers are practically eliminated, and full length, soft fiber produced.

The digester provided by the present invention, while applicable to digestion processes generally, is especially adapted for use in the fiber-liberating step of the process cov-' ered by the copending application referred to above.

Having reference now to the drawings, the digester may be, and preferably is, of the form usually employed in wood treating processes. It comprises a vertically disposed cylindrical shell 1 provided with end memhere 2 and 3 integrally connected thereto, as by welding or riveting, and a jacket 4 connected to the shell, to provide a steam chamber 5 surrounding substantially the entire body thereof. The jacket is provided with a steam inlet 6 and outlet 7. A manhole 8 is provided in the upper end of the digestcr through which material to be treated may be passed, this opening being closed in any suitable manner, as for example by means of a cover 8a bolted thereto. The shell is also provided with a discharge valve 9, of any suitable type, centrally disposed in bottom member 3, and a thermometer 10, steam gage 11, and safety valve 12 are disposed in top member 2.

A sheet metal funnel member 13, arranged in the lower end of the digester in the manner shown in Fig. 1, guides the contents of the apparatus into the discharge valve. A steam coil 14 may be disposed below the funnel member to heat the lower portion of the charge, which does not receive heat directly from the steam jacket in. the form shown. A pipe 15 bent in the form of a ring of substantially the same diameter as the inside of shell 1 and provided along its length with perforations 15a, Fig. 3, is horizontally disposed inside the shell above the middle for the purpose of distributing a digesting liquid uniformly over the material which is to be processed. Coil 15 is connected to a reagent supply, for example to a line 16 and also to a pipe 17 through which a chemical reagent may be introduced.

Various means may be employed for confining the free surface of a charge of wood or other material placed in the digester, and for compacting the. mass during digestion. Because of its simplicity and etticiency, the means illustrated is preferred. This means comprises a circular plate 18 of substantially the inner diameter of shell 1 suspended in the upper end of the digester from a cable 19 centrally connected to the plate.

In order to permit the plate to move readil v without becoming askew and binding, four grooved rollers 20 are journalled at 90 intervals around the edge of the under side of the plate, the grooves of the rollers engaging V-shaped guides 21 crannected to'the interior and extending dowiiwardly from the top of the shell. Downward movement of the plate is limited by flared stops 22 formed on the lower end of guides 21. These guides are long enough to permit the plate to move downwardly and compact a given charge of material, due regard being had to variations in size of charge and in bulk due to digestive changes. An opening covered by a hinged door 23 is provided in the plate, to lie below manhole 8, to permit material passed into the digester to fall therethrough into the bottom of the digester.

As shown in Fig. 2 the plate is provided with a plurality of perforations 24 which permit circulation of steam or other fluid formed during digestion, thus equalizing fluid pressure in the digester and preventing excess pressure in the charge. Preferably these perforations are of progressively larger diameter toward the edge of the plate from the center, in order to cause uniformity of fiuid circulation and fluid pressure. All of the holes are small enough, however, so that no substantial amount of the material being treated is able to pass thercthrough.

According to the invention of the copending application referred to hereinabove, the wood to be pulped is compacted during the digestion. This may be accomplished by making the plate 18 sufliciently heavy to exert the desired or necessary pressure on the upper, or free, surface of the wood. However, it is preferred to use a relatively light plate, say one inch in thickness, and to uniformly arrange weights 25 on the upper side thereof, the total weight being sufficient to produce the necessary compacting. The weights are preferably arranged over the rollers 20. Cable 19 is passed over sheaves 26 and connected to a counterweight 27 to assist in raising and lowering the weight at the beginning and end of the cook.

The use of this apparatus may be described in connection with my aforemem tioned copending application. Wood and wood waste of any kind, including the bark, is preliminarily softened by digestion with lime, and a suitable charge of the treated tion, and for most purposes it is preferred to use a solution of 15 pounds of caustic soda in gallons of water 'to each 100 pounds of lime-softened wood. Manhole 8 and the door 23 in plate 18 are closed, and weighted plate 18 is lowered to compact the wood elow it. Steam is passed into jacket 5, to indirectly heat the contents of the digester, and the charge is cooked for a suflicient length of time to cause solution of the incrustants and liberation of the fiber.

As the charge heats, the wood may expand, due to the heating and penetration by the liquor. The pressure of the weight, however, opposes this change of bulk. If the expansion pressure is great enough, the plate rises, but its pressure is constantly applied to the upper surface of the charge. Likewise, if the mass shrinks because of the digestion process, or for other reasons, the plate follows the material. In consequence, the compacting pressure is always applied to the charge, and that pressure is great enough to prevent other than slow volume changes. That is, itprevents agitation by either boiling of the liquor or by reason of reaction of the liquor on the wood. It is by virtue of this feature that the benefits of the invention are obtained.

In the case of most woods. cooking will re quire about one and one-half hours digestion after the pressure in the digester has attained 125 pounds gauge, the pressures employed in general not exceeding 160 pounds gauge. When cooking is completed, the pressure in the digester is relieved. as through safety valve 12, the liquor is withdrawn through a draw-off pipe 28 in the bottom of the digester. and the pulped contents are discharged through valve 9. Gravity will usually suffice to evacuate the contents of the digester, but if desired or necessary, pressure may be applied from above by means of air supply pipes 29 connected to the upper part of the shell.

By the use of this digester, the time required for cooking is reduced very materially, and the pulp produced is substantially free from the disadvantages of that produced by.

prior processes. Using the soda process, I obtain a pulp composed of soft, strong pure cellulose .fibers which retain substantially their natural characteristics and length, and which are much longer than those previously produced by the soda process. The yields of pulp are also materially greater.

I claim: 1. An apparatus for digesting wood and the like comprising a shell, means associated with said shell for maintaining a charge of said material compact during digestion," means for withdrawing digested material from the bottom of the shell and means for indirectly heating said charge;

2fAn apparatus for digesting wood and the like comprising a shell having a jacketed body portion, a closable charging port in its upper end, a discharge valve in its lower end, and a vertically movable plate adapted to cover the entirefree surface of a charge of.

said material and to maintain it compact during digestion. I

3. An apparatus for digesting wood and the like comprising a shell having a jacketed body portion, a closable charging port in its upper end, a discharge valve in its lower end, means for introducing and uniformly distributing a liquid digestant in said shell, and a weighted plate for constantly applying pressure to the entire surface of a charge of said material during digestion.v

4. An apparatus for digesting wood and the like comprising a vertically disposed cylindrical. shell provided with integral end members and having a jacketed body portion, a closable opening in the top for charging said shell, a discharge valve in the bottom, and a vertically movable weighted plate of substantially the inner diameter of said shell centrally suspended in the upper end thereof for compacting a charge of said material during digestion, said plate being provided with a plurality of perforations to permit fluid circulation without permitting any substantial amount of said material to pass therethrough.

5. An apparatus for digesting wood and the like comprising a vertically disposed cylindrical shell provided with integral end members and having a jacketed body portion, a closable opening in the top for charging said shell, a discharge valve in the bottom, and a vertically movable weighted plate of substantially the inner diameter of said shell suspended in the upper end thereof by a cable centrally attached to the plate, said plate constantly maintaining said material compact during digestion, said plate being provided with a plurality of perforations of progressively smaller diameter from the edge toward the center of the plate for permitting uniform fluid pressure distribution, said perforations being small enough to prevent passage of any substantial amount of said material therethrough.

In testimony whereof, I hereunto sign my name.

PAUL e. VON HILDEBRANDT, 

